Engine cooling system for vehicle

ABSTRACT

In order to reduce driving power of an engine cooling system in which a cooling fan for cooling a radiator and a water pump are driven by a motor, according to the invention, a pump motor of the water pump  5  which circulates liquid coolant is used as a drive source of the cooling fan. An electromagnetic clutch is provided between the pump motor and the cooling fan, and when the liquid coolant exiting from an engine is at a predetermined temperature or higher, the electromagnetic clutch is brought into a connected state, whereas when the liquid coolant is at a temperature lower than the predetermined temperature, the electromagnetic clutch is brought into a disconnected state. When the liquid coolant is at a temperature lower than the predetermined temperature, and the vehicle speed is at a predetermined speed or higher, the electromagnetic clutch is brought into a connected state, and a rotational force of the cooling fan receiving driving wind is transmitted to the pump motor to reduce its load.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an engine cooling system for a vehicle having the structure in which liquid coolant of an engine is cooled by a radiator, and particularly to an engine cooling system in which a cooling fan for cooling the radiator is driven by a motor of a water pump for circulating the liquid coolant.

2. Description of Related Art

In a cooling system of an engine of a vehicle, liquid coolant is basically circulated in such a manner that the liquid coolant of which temperature rises as a result of cooling the engine is fed by a water pump to a radiator, where the cooling water is cooled by wind during running and by air blowing from a cooling fan, and thereafter, the liquid coolant is returned to the engine again.

The cooling of the engine is performed for the purpose of preventing overheating, but if the engine is excessively cooled, thermal loss of the engine increases, and mechanical loss due to increase of friction in sliding parts such as bearings and piston rings increases. Therefore, it is desirable to perform proper cooling with minimum energy.

According to a prior art example relating to cooling of an engine, in the case of a method in which a water pump and a cooling fan are driven by the engine (hereinafter, called a prior art example 1), there has been a first defect of consuming power for driving the cooling fan wastefully since the cooling fan is driven even when cooling by the radiator is possible by natural convection of the liquid coolant and an air flow obtained by running of the vehicle. Further, there has been a second defect of consuming useless energy since the water pump also has a high rotational speed following the engine speed and circulates the liquid coolant more than necessary at the time of high speed cruising.

As an improved example of this, as described in Automotive Engineering Handbook 4 Design (Power Train) Version, Society of Automotive Engineers of Japan, 2005, p. 65-66), there has been a method in which the cooling fan is driven by a motor, and the operation of the cooling fan is controlled in accordance with the cooling state of the engine (hereinafter, called a prior art example 2), which is generally carried out. According to the method, the above described first defect can be eliminated, but the above described second defect remains. Furthermore, there has been carried out a method in which the water pump and the cooling fan are driven by individual motors and the individual rotational speeds are controlled in accordance with the cooling state of the engine (hereinafter, called a prior art example 3). According to this, the above described first and second defect can be both eliminated.

As another example relating to a method of driving a cooling fan, in addition to the above described methods, it is considered that the cooling fan is driven with the motor directly connected to the water pump for hot water which circulates the hot water of a heat accumulator for heater, for example, in JP-A-2002-97956. Specifically, when the cooling fan is rotated, the impeller of the water pump for hot water is also rotated, but the impeller itself is rotated reversely so as not to circulate the hot water. When the hot water is circulated, the motor is rotated reversely from the above described case so that the water pump for hot water circulates the hot water, but the cooling fan is not caused to rotate by using a power transmission selecting means. According to this, at the time of circulation of the hot water, the cooling fan does not rotate, and therefore, noise and drive power of the air-cooling fan can be reduced. However, in this constitution, when the temperature of the engine becomes high and the cooling fan is driven accordingly, the power which circulates the liquid coolant does not occur since the water pump for hot water rotates in the reverse direction from the pump operation, but energy loss occurs due to the impeller rotating in the hot water and the same defect as the prior art example 2 arises.

BRIEF SUMMARY OF THE INVENTION

Cooling of an engine is performed by circulating liquid coolant which has liquid-cooled the engine with a water pump and by air-cooling the liquid coolant with a radiator as described above. The liquid coolant which directly cools the engine needs to be circulated substantially continuously during operation of the engine. Accordingly, during the operation of the engine, the water pump is operated substantially at all times. Meanwhile, in the radiator, wind hits against the radiator due to running of the vehicle when the vehicle runs. Hereinafter, the wind will be called driving wind. The velocity of the driving wind passing through the radiator is about 20 to 30% of the vehicle speed, and therefore, at the time of intermediate and high speed cruising, the liquid coolant can be cooled sufficiently only with the driving wind in general, even if the cooling fan is not rotated. Therefore, the time in which the cooling fan needs to be operated is as short as about 10% of the total operation time of the engine while it depends on the running condition of the vehicle and the atmospheric temperature.

During most of the period in which the vehicle is running, the radiator is sufficiently cooled only by the driving wind in this manner. While the vehicle is running, the cooling fan also receives rotational force from the driving wind. However, in the prior art examples 1, 2 and 3 and especially in the prior art examples 2 and 3 of JP-A-2002-97956 and in JP-A-2002-97956, the cooling fan is reduced in its drive power since it receives the rotational force from the driving wind, but its effect is limited to the time when the cooling fan is driven. Considering that the required operating time of the cooling fan is short as described above, the substantial effect of the driving wind is small.

The present invention is made in view of the above described circumstances, and its object is to provide an engine cooling system for a vehicle configured so that a cooling fan of a radiator and a water pump are driven by a motor, which can reduce power required for cooling by assisting power of the water pump by using rotational force of the cooling fan obtained by driving wind to drive the water pump even when drive of the cooling fan is stopped since the cooling water can be sufficiently cooled by the driving wind.

(Prerequisite Constitution of the Invention)

The engine cooling system for a vehicle includes a water pump for circulating liquid coolant of an engine, a radiator which cools the liquid coolant, and a cooling fan which cools the radiator. The present invention presupposes that a motor (pump motor) is used as a drive source of the water pump, and the cooling fan is rotationally driven by utilizing rotation of the pump motor. A clutch for connecting and disconnecting the cooling fan to and from the pump motor is provided, and the clutch is controlled to be connected and disconnected by a control means

(First Means of the Invention)

In order to achieve the above described object, in the first means (claim 1) of the present invention, a temperature detecting means that detects a temperature of the liquid coolant is provided, so that it can be judged whether or not the radiator needs to be forcefully cooled by the operation of the cooling fan by the detected temperature of the temperature detecting means when the liquid coolant is cooled by the radiator.

Further, the present invention is provided with an assist ability detecting means that detects whether or not the cooling fan has assist ability for the pump motor when the cooling fan rotates by receiving external wind pressure (including driving wind pressure). In this case, the assist ability is the ability of the cooling fan allowing the rotational force to be transmitted to the pump motor, in such a manner that when the cooling fan is forcefully rotated by receiving the external wind pressure, if the rotational speed of the cooling fan exceeds the speed at which the pump is rotated by the pump motor, the cooling fan can reduce the load of the pump motor by transmitting the rotation of the cooling fan to the pump motor.

The control means causes the clutch to perform a connecting operation to connect the pump motor and the cooling fan when a detected temperature of the temperature detecting means is a predetermined temperature or higher, or when the detected temperature of the temperature detecting means is lower than the predetermined temperature and the assist ability detecting means detects presence of the assist ability, and the control means causes the clutch to perform a disconnecting operation to disconnect the pump motor from the cooling fan when the detected temperature of the temperature detecting means is lower than the predetermined temperature and the assist ability detecting means detects absence of the assist ability.

Thus, according to the first means, when the radiator needs to be cooled by the cooling fan (or when the detected temperature of the temperature detecting means is a predetermined temperature or higher), the clutch is brought into a connected state so that the cooling fan is rotationally driven by the pump motor. When the radiator does not need to be cooled by the cooling fan, the clutch is disconnected in principle so that the pump motor does not rotationally drive the cooling fan, and therefore, the pump motor is not operated wastefully.

In addition, even when the radiator does not need to be cooled by the cooling fan, if the cooling fan has the assist ability, the clutch is brought into a connected state, and therefore the rotation of the cooling fan which is forcefully rotated by the external wind pressure is transmitted to the pump motor to be able to reduce the load on the pump motor. When the radiator needs to be cooled by the cooling fan, the clutch is in a connected state. Therefore, if the cooling fan is in the state of having the assist ability at this time, the pump motor can be driven by the cooling fan which is forcefully rotated by the external wind pressure, and the load on the pump motor can be reduced.

In the first means, the assist ability detecting means can be constituted of a vehicle speed sensor that detects the speed of the vehicle, and a determining means that determines the assist ability is present when a detected speed of the vehicle speed sensor is a predetermined speed or higher, and determines that the assist ability is absent when the detected speed of the vehicle speed sensor is lower than the predetermined speed (claim 2).

Further, the assist ability detecting means may be constituted of a motor rotational speed detecting means that detects the rotational speed of the pump motor, a vehicle speed sensor that detects the speed of the vehicle, and a determining means that calculates to convert a detected speed of the vehicle speed sensor into a rotational speed of the cooling fan, and determines that the assist ability is present when the rotational speed exceeds the rotational speed of the pump motor detected by the motor rotational speed detecting means, and determines that the assist ability is absent when the rotational speed of the cooling fan is the rotational speed of the pump motor or lower (claim 3)

Further, the assist ability detecting means may be constituted of a fan rotational speed detecting means that detects the rotational speed of the cooling fan, a motor rotational speed detecting means that detects the rotational speed of the pump motor, a vehicle speed sensor that detects the speed of the vehicle, and a determining means that determines that the assist ability is present when the rotational speed of the cooling fan detected by the fan rotational speed detecting means exceeds the rotational speed of the pump motor detected by the motor rotational speed detecting means, and determines that the assist ability is absent when the vehicle speed sensor detects a speed that is a predetermined speed or lower (claim 4).

(Second Means of the Invention)

In order to attain the above described object, in the second means of the present invention (claim 5), the clutch is brought into a connected state to rotationally drive the cooling fan by the pump motor when the radiator needs to be cooled by the cooling fan (or when a detected temperature of the temperature detecting means is a predetermined temperature or higher), and the clutch is brought into a disconnected state so as not to rotationally drive the cooling fan by the pump motor when the radiator does not need to be cooled by the cooling fan. A one-way clutch is provided between the pump motor and the cooling fan, so as to transmit the rotation of the cooling fan to the pump motor by the one-way clutch when the cooling fan receives external wind pressure and tends to rotate faster than the pump motor (namely, when assist ability is present), irrespective of the connected or disconnected state of the clutch.

According to the second means, when the radiator does not need to be cooled by the cooling fan, the clutch is disconnected so that the cooling fan is not rotationally driven by the pump motor, and when the cooling fan is rotated by the external wind dynamic pressure and has the assist ability, the rotation of the cooling fan is automatically transmitted to the pump motor to reduce the load of the pump motor, by the operation of the one-way clutch.

(Additional Constitutions to First and Second Means)

In the present invention, the following constitutions can be added to the above described first means and second means.

The rotational speed of the pump motor may be changed to be higher and lower in accordance with a degree of the detected temperature of the temperature detecting means (claims 6 and 7). The rotational speed of the pump motor may be changed to be higher and lower in accordance with a degree of the difference in temperature of the liquid coolant on an inlet port side and an outlet port side of the engine (claims 8 and 9). When the rotational speed of the pump motor is changed like this, the rotational speed of the cooling fan can be made higher when the liquid coolant needs to be more intensively cooled with the radiator.

Transmission of rotation from the pump motor to the water pump can be constituted to be performed by a magnetic coupling (claims 10 and 11). According to the constitution, the pump motor and the water pump can be shielded from each other without using a mechanical seal. Therefore, leakage of the liquid coolant in the power transmission portion to the water pump from the pump motor is eliminated, and friction loss by a seal can be reduced.

Starting of the pump motor may be delayed so as to be later than the start of the engine (claims 12 and 13). By doing so, the pump motor is started so as to avoid the engine starting time during which a large amount of current flows into a starter motor, and therefore, the load on the battery of the vehicle can be reduced.

Further, a cooling fan for cooling the radiator or a body such as a condenser of an air conditioner to be cooled other than the radiator is provided separately from the cooling fan, and a motor which drives the other cooling fan may be constituted of a motor generator which functions as a generator when receiving a rotational force from the other cooling fan when the other cooling fan does not need to be driven (claims 14 and 15). By doing so, when the above described other cooling fan rotates by external wind dynamic pressure, electric power is generated by the motor generator to be able to charge the battery of the vehicle.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a vertical sectional view of a main part, showing a first embodiment of the present invention;

FIG. 2 is a side view showing an entire cooling system;

FIG. 3 is a schematic diagram of piping of the cooling system;

FIG. 4 is a block diagram showing a control configuration;

FIG. 5 is a flowchart for control of an electromagnetic clutch;

FIG. 6 is a diagram corresponding to FIG. 4 and showing a second embodiment of the present invention;

FIG. 7 is a flowchart corresponding to FIG. 5;

FIG. 8 is a flowchart corresponding to FIG. 5 and showing a third embodiment of the present invention;

FIG. 9 is a view corresponding to FIG. 1 and showing a fourth embodiment of the present invention;

FIG. 10 is a diagram corresponding to FIG. 4;

FIG. 11 is a flowchart corresponding to FIG. 5;

FIG. 12 is a view corresponding to FIG. 1 and showing a fifth embodiment of the present invention; and

FIG. 13 is a view corresponding to FIG. 2 and showing a sixth embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION First Embodiment

Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. 1 to 5. FIG. 2 schematically shows a configuration of a cooling system of an engine, for example, a gasoline engine, as a propulsion source of a vehicle. As shown in FIG. 2, a jacket 2 is formed in an engine 1, and cooling of the engine 1 is performed by liquid coolant passing inside the jacket 2. The engine cooling system is a system which cools the engine 1 by circulating the liquid coolant, of which temperature has risen by cooling the engine 1, and which is cooled outside and returned to the engine 1 again, and includes a radiator 3, a cooling fan 4, a water pump 5 and a pump motor 6 which drives the water pump 5.

The above described pump motor 6 is fixed to a support frame 7 mounted to a rear portion of the radiator 3. The pump motor 6 is constituted of, for example, a brushless DC motor, and includes a stator 9 fixed to a motor case 8, and a rotor 11 rotatably supported by the motor case 8 via a bearing 10. Both end portions of a rotary shaft 12 of the rotor 11 are projected to both front and rear sides from the motor case 8. The stator 9 is formed by winding a coil 9 b in a plurality of phases around a stator core 9 a. The rotor 11 is of a permanent magnet type which is formed by attaching a permanent magnet 11 b which is magnetized into a plurality of poles to an outer periphery of a rotor core 11 a.

The above described water pump 5 is mounted to the rear portion of the pump motor 6. The water pump 5 is constituted as a centrifugal type, and an impeller 14 in a casing 13 thereof is fixed to the rear end portion of the rotary shaft 12 of the pump motor 6. A space between the water pump 5 and the pump motor 6 is sealed with a mechanical seal 15 so that the liquid coolant does not leak to the pump motor 6 side. The mechanical seal 15 is constituted of a seat 16 provided at the impeller 14, a seal ring 19 which is pressed against the seat 16 by a bellows spring 18 which is provided at a partition plate 17 which partitions the water pump 5 and the pump motor 6, and the seat 16 slides with respect to the seal ring 19.

The above described cooling fan 4 is rotatably supported at a front end portion of the rotary shaft 12 of the pump motor 6 via a bearing 20. A clutch, for example, an electromagnetic clutch 21 is provided between the cooling fan 4 and the pump motor 6. The electromagnetic clutch 21 includes a clutch plate 22 fixed to the rotary shaft 12, a clutch plate 24 of a magnetic material such as iron which is mounted movably in an axial direction, by a pin 23 provided to project to the cooling fan 4 side, and an electromagnetic coil 25 fixed to the motor case 8 of the pump motor 6.

When the above described electromagnetic coil 25 is switched on, the clutch plate 24 of the cooling fan 4 is attracted to the clutch plate 22 of the rotary shaft 12 by the magnetic force and is brought into a connected state, and the rotary shaft 12 of the pump motor 6 and the cooling fan 4 are connected. When the electromagnetic coil 25 is switched off, the attraction of the clutch plate 24 of the cooling fan 4 to the clutch plate 22 is released to cause a disconnected state, and connection of the rotary shaft 12 of the pump motor 6 and the cooling fan 4 is released.

The above described water pump 5 is provided for circulating the liquid coolant, and its inlet port 5 a is connected to an outlet port 2 a of the jacket 2 of the engine 1 by a hose 26, and a discharge port 5 b is connected to an inlet port 27 a of a thermo valve 27 via a hose 28, as shown in FIG. 3. The thermo valve 27 has two outlet ports 27 b and 27 c, and while the temperature of the liquid coolant is low, the thermo valve 27 is in the state in which the outlet port 27 c is opened and the outlet port 27 b is throttled. The thermo valve 27 is constituted so that when the temperature of the liquid coolant rises, the outlet port 27 b is opened whereas the outlet port 27 c is throttled. The outlet port 27 b of the thermo valve 27 is connected to an inlet port 3 a of the radiator 3 via a hose 29, and the other outlet port 27 c is connected to an inlet port 2 b of the jacket 2 of the engine 1 via a hose 30. Further, an outlet port 3 b of the radiator 3 is also connected to the inlet port 2 b of the jacket 2 of the engine 1 via a hose 31.

FIG. 4 is a block diagram showing a control configuration of the cooling system Control of the cooling system is carried out by a control circuit 32 as a control means with, for example, a microcomputer (not shown) as a main component, to which a liquid temperature sensor 33 as a temperature detection means of the liquid coolant, a vehicle speed sensor 34, an inverter driving apparatus 35 and the like as well as the electromagnetic coil 25 of the above described electromagnetic clutch 21 are connected.

The above described liquid temperature sensor 33 detects the temperature of the liquid coolant in the outlet port 2 a of the jacket 2, for example. The vehicle speed sensor 34 is provided for detecting the speed of the vehicle, detects the rotational speed of the axel, for example, and inputs the detected output power into the control circuit 32. The control circuit 32 is configured to calculate the vehicle speed by the rotational speed detected by the vehicle speed sensor 34 and the tire diameter which is stored in a memory (not shown) in advances.

The inverter driving apparatus 35 is provided for inverter-driving the pump motor 6, and a battery 36 of the vehicle is used for its direct-current power source. The control of the rotational speed of the pump motor 6 is carried out by a pulse width modulation (PWM) method. Therefore, the pump motor 6 is provided with, for example, a frequency generator 37 as a rotational speed detecting means for detecting its rotational speed, and the detected output is inputted into the control circuit 32. The control circuit 32 compares the rotational speed of the pump motor 6 which is detected by the frequency general or 37 and the set rotational speed which is set in advance, and gives a drive signal corresponding to the velocity deviation to the inverter driving apparatus 35. Then, the inverter driving apparatus 35 forms a PWM signal corresponding to the velocity deviation given from the control circuit 32 to control the pump motor 6 to be at the set rotational speed. The set rotational speed is stored in the memory (not shown) which the control circuit 32 has.

Next, operation of the above described configuration will be described. First, in this embodiment, it is determined whether or not the liquid coolant needs to be forcefully cooled on the basis of the detected temperature of the liquid temperature sensor 33. Specifically, when the liquid temperature sensor 33 detects the predetermined temperature or higher, it is determined that forced cooling is needed. When the forced cooling is needed, the cooling fan 4 is connected to the rotary shaft 12 of the pump motor 6, and the cooling fan 4 is rotationally driven by the pump motor 6.

When the speed of the vehicle is at a predetermined speed or higher, the cooling fan 4 receives driving wind dynamic pressure (external air pressure) and is made rotate faster than the rotational speed of the pump motor 6. Therefore, it is determined that the load on the pump motor 6 can be reduced (namely, assist ability is present) by transmitting the rotation of the cooling fan 4 to the pump motor 6, and the cooling fan 4 is connected to the rotor shaft 12 of the pump motor 6. The vehicle speed when it is determined that the assist ability is present is set at the vehicle speed obtained in advance by the experiment and is stored in the memory of the control circuit 32. In this embodiment, the correlation of the vehicle speed and the rotational speed of the cooling fan 4 is obtained in advance by the experiment, and when the rotational speed of the cooling fan 4 by the driving wind is higher as compared with the set rotational speed of the pump motor 6, it is determined that the cooling fan 4 can assist the power of the pump motor 6.

Cooling of the liquid coolant will be explained hereinafter. First, an ignition switch not shown is operated to start the engine 1. Thereupon, the control circuit 32 actuates the pump motor 6 simultaneously with the start of the engine 1 to circulate the liquid coolant of the engine 1. At the beginning of the start of the engine 1, the engine 1 is not sufficiently warmed, and therefore, the outlet port 27 b of the thermo valve 27 is closed. Therefore, the liquid coolant circulates through the hose 26, the water pump 5, the hose 28, the thermo valve 27 and the hose 30 from the outlet port 2 a of the jacket 2 to be returned to the inlet port 2 b of the jacket 2, and is not fed to the radiator 3.

When the engine 1 is warmed and the temperature of the liquid coolant rises, the thermo valve 27 throttles the outlet port 27 c to open the outlet port 27 b, the liquid coolant circulates in the jacket 2 and the radiator 3. Specifically, the liquid coolant in the jacket 2 circulates through the hose 26, the water pump 5, the thermo valve 27, the hose 29, the radiator 3 and the hose 31 in sequence from the outlet port 2 a of the jacket 2 to return to the jacket 2. The liquid coolant which has cooled the engine 1 and is at a high temperature is cooled when it passes through the radiator 3.

With the start of the engine 1, the control circuit 32 starts to execute an electromagnetic clutch control routine of FIG. 5. Specifically, the control circuit 32 firstly brings the electromagnetic clutch 21 into a disconnected state as an initial setting when it starts the electromagnetic clutch control routine in FIG. 5 (step S1). Next, the control circuit 32 obtains the detected temperature of the liquid temperature sensor 33 (step S2), and determines whether or not the temperature is at a predetermined temperature T (° C.) or higher (step S3). When it is the time soon after the start of the engine 1, the liquid coolant does not rise in temperature so much, and the detected temperature of the liquid temperature sensor 33 is lower than T. Therefore, the control circuit 32 determines that forced cooling by the cooling fan 4 is not needed (“NO” in step S3).

When it is determined that forced cooling is not needed, the control circuit 32 obtains the detected speed of the vehicle speed sensor 34 in order to connect or disconnect the electromagnetic clutch 21 in accordance with presence or absence of the assist ability of the cooling fan 4 (step S4), and determines whether or not the speed of the vehicle is at a predetermined speed V (km/s) or higher (step S5: an assist ability detecting means, a determining means). Incidentally, when the vehicle starts to travel, the cooling fan 4 receives driving wind pressure and rotates when the electromagnetic clutch 21 is in the disconnected state. In this case, when the speed of the vehicle is lower than the predetermined speed V, even if the cooling fan 4 rotates by receiving the driving wind pressure, the rotational speed of the cooling fan 4 does not become the rotation frequency of the pump motor 6 or higher, and therefore, the control circuit 32 determines that the assist ability is not present (“NO” in step S5), and keeps the electromagnetic clutch 21 in the disconnected state (step S6).

When the speed of the vehicle becomes the predetermined speed V or higher, the cooling fan 4 which rotates by receiving the driving wind pressure rotates at a rotational speed which is the rotational speed of the pump motor 6 or higher. Thereupon, the control circuit 32 determines that the cooling fan 4 rotating by receiving the driving wind pressure has the assist ability (“YES” in step S5), and energizes the electromagnetic coil 25 and brings the electromagnetic clutch 21 into a connected state (step S7). When the electromagnetic clutch 21 is in the connected state, the rotation of the cooling fan 4 is transmitted to the rotor shaft 12 of the pump motor 6 via the clutch plates 24 and 22 of the electromagnetic clutch 21. Therefore, the load of the pump motor 6 which drives the water pump 5 is reduced by the amount of the rotational force received from the cooling fan 4 (the motor assist).

After some time lapses from the start of the engine 1, the temperature of the liquid coolant rises. When the temperature of the liquid coolant in the outlet port 2 a of the jacket 2 becomes the predetermined temperature T or higher, the control circuit 32 determines that the radiator 3 needs to be forcefully cooled (“YES” in step S3), and switches on the electromagnetic coil 25 to bring the electromagnetic clutch 21 into a connected state (step S8). Thereby, the rotation of the pump motor 6 is transmitted to the cooling fan 4 via the clutch plates 22 and 24, and the cooling fan 4 is rotationally driven.

When the temperature of the liquid coolant in the outlet port 2 a of the jacket 2 is the predetermined temperature T or higher, the electromagnetic clutch 21 is kept in the connected state irrespective of whether or not the speed of the vehicle is the predetermined speed V or higher. Therefore, when the speed of the vehicle is the predetermined speed V or higher, the cooling fan 4 has the assist ability, but the electromagnetic clutch 21 is in the connected state, and thereby the rotation of the cooling fan 4 by the driving wind pressure is automatically transmitted to the pump motor 6 to reduce the load.

Incidentally, for example, during intermediate and high speed traveling, the radiator 3 is cooled by the driving wind, and therefore, in the ordinary case, the temperature of the liquid coolant in the outlet port 2 a of the jacket 2 becomes lower than the predetermined temperature T even if the cooling fan 4 is not rotationally driven by the pump motor 6. In this state, the control circuit 32 performs control of connecting or disconnecting the electromagnetic clutch 21 in accordance with the presence or absence of the assist ability of the cooling fan 4 as described above.

Specifically, when the detected temperature of the liquid temperature sensor 33 becomes lower than the predetermined temperature T (“NO” in step S3), the control circuit 32 determines whether or not the detected speed of the vehicle speed sensor 34 is the predetermined speed V or higher (steps S4, S5). The control circuit 32 determines that the cooling fan 4 has the assist ability when the speed of the vehicle is V or higher (“YES” in step S5), and switches on the electromagnetic coil 25 to keep the electromagnetic clutch 21 in the connected state Thereby, the rotation of the cooling fan 4 is transmitted to the pump motor 6, and reduces the load on the pump motor 6 which drives the water pump 5. When the speed of the vehicle is lower than V, the control circuit 32 brings the electromagnetic clutch 21 into a disconnected state (step S6) so that the pump motor 6 does not rotationally drive the cooling fan 4 wastefully.

When the vehicle stops and the ignition switch is operated to be off, the engine 1 is stopped, and according to this, the pump motor 6 is switched off to stop the water pump 5. The control circuit 32 also stops execution of the electromagnetic clutch control routine in FIG. 5. In this manner, according to this embodiment, the pump motor 6 is used as a drive source of the cooling fan 4, and both are connected and disconnected by the electromagnetic clutch 21, and therefore, the cooling fan 4 is not driven by the pump motor 6 when the radiator 3 does not need to be forcefully cooled by the cooling fan 4.

In addition, if the cooling fan 4 which receives the driving wind dynamic pressure has the assist ability when the radiator 3 needs to be forcefully cooled by the cooling fan 4, the rotation of the cooling fan 4 is transmitted to the pump motor 6 via the electromagnetic clutch 21 in the connected states and therefore, the load on the pump motor 6 is reduced. In addition, even when the radiator 3 does not need to be forcefully cooled with the cooling fan 4, if the cooling fan 4 receiving the driving wind dynamic pressure has the assist ability, the rotation of the cooling fan 4 is transmitted to the pump motor 6 by switching the electromagnetic clutch 21 into the connected state from the disconnected state, and therefore, the load on the pump motor 6 can be reduced as described above.

Accordingly, as compared with the cooling system with the constitution in which the electromagnetic clutch 21 is brought into the connected state when the radiator 3 needs to be forcefully cooled and the electromagnetic clutch 21 is brought into the disconnected state when the radiator 3 does not need to be forcefully cooled, the load on the pump motor 6 can be reduced by transmitting the rotation of the cooling fan 4 to the pump motor 6 by bringing the electromagnetic clutch 21 into the connected state when the cooling fan 4 has the assist ability even if the radiator 3 is cooled by the driving wind and does not need to be forcefully cooled by the cooling fan 4 especially during intermediate and higher speed traveling of the vehicle, and the fuel saving of the engine 1 can be enhanced correspondingly.

Second Embodiment

FIGS. 6 and 7 show a second embodiment of the present invention. The point in which the second embodiment differs from the above described first embodiment is that the presence or absence of the assist ability of the cooling fan 4 is determined by comparing the rotational speed of the cooling fan 4 and the rotational speed of the pump motor 6.

Specifically, in this embodiment, the vehicle speed sensor 34 is not included as shown in FIG. 6, and instead of this, a rotational speed sensor 38 as a fan rotational speed detecting means for detecting the rotational speed of the cooling fan 4. Although it is not shown, the rotational speed sensor 38 is constituted of a permanent magnet provided at the cooling fan 4, for example, and a magnetism detecting element such as a hall element provided at the support frame 7, for example, for detecting the magnetism of the permanent magnet, and the magnetism detecting element outputs the number of pulses corresponding to the rotational speed of the cooling fan 4. The control circuit 32 calculates the rotational speed of the cooling fan 4 based on the number of pulses inputted from the rotational speed sensor 38.

In an electromagnetic clutch control routine shown in FIG. 7, when the temperature in the outlet port 2 a of the jacket 2 of the liquid coolant is lower than the predetermined temperature T (“NO” in step A3), and the radiator 3 does not need to be forcefully cooled by the cooling fan 4, the control circuit 32 obtains the detected rotational speed of the rotational speed sensor 38 (step A4). Subsequently, the control circuit 32 obtains the rotational speed of the pump motor 6 from the frequency generator 37 as a motor rotational speed detecting means, and when the rotational speed of the cooling fan 4 is the rotational speed of the pump motor 6 or lower, the control circuit 32 determines that the cooling fan 4 does not have the assist ability (“NO” in step A5: the determining means), and brings the electromagnetic clutch 21 into the disconnected state (step A6). When the rotational speed of the cooling fan 4 exceeds the rotational speed of the pump motor 6, the control circuit 32 determines that the cooling fan 4 has the assist ability (“YES” in step A5: the determining means) and brings the electromagnetic clutch 21 into the connected state (step A7).

When the rotational speed of the pump motor 6 is controlled to be the set rotational speed which is set in advance as in this embodiment, the control circuit 32 may be configured to obtain the set rotational speed which is stored in a memory not shown of the control circuit 32 (a motor rotational speed detecting means) and not to obtain the rotational speed of the rotational speed sensor 38. In the case of the configuration where the rotation of the pump motor 6 is transmitted to the cooling fan 4 via a speed-reduction mechanism, the output rotational speed of the speed-reduction mechanism becomes the rotational speed of the pump motor 6. Presence or absence of the assist ability of the cooling fan 4 is determined on the basis of a judging standard which is the ratio of the rotational speed of the cooling fan 4 due to the driving wind with respect to the rotational speed of the pump motor 6 as described above. However in order to prevent the connection of the cooling fan 4 and the pump motor 6 from being frequently turned on and off, the judging value includes such a dead zone as is used in conventional on-off control. Specifically, the upper limit value and the lower Limit value are set at the rotational speeds of the cooling fan (or at the vehicle speeds when using the correlation of the vehicle speed and the rotational speed of the cooling fan) at which the cooling fan 4 and the pump motor 6 are connected and disconnected respectively by the electromagnetic clutch 21, and control is performed by connecting those at the upper limit value and disconnecting those at the lower limit value.

Third Embodiment

FIG. 8 shows a third embodiment of the present invention. This embodiment differs from the above described second embodiment in the point that presence or absence of the assist ability of the cooling fan 4 is determined by calculating the rotational speed of the cooling fan 4 due to the driving wind from the driving speed of the vehicle, and by comparing the calculated rotational speed of the cooling fan 4 and the rotational speed of the pump motor 6. Accordingly, in this embodiment, the rotational speed sensor 38 in the second embodiment is not included, but the vehicle speed sensor 34 in the first embodiment is included instead.

Specifically, when determining whether or not the cooling fan 4 has the assist ability, the control circuit 32 obtains the detected speed of the vehicle speed sensor 34 (step a4 in FIG. 8), and calculates the rotational speed of the cooling fan 4 due to the driving wind based on the detected speed (step a5). The detected speed (speed of the vehicle) of the vehicle speed, sensor 34 and the rotational speed of the cooling fan 4 may be obtained by an experiment in advance and stored in a storage means, and when the detected speed of the vehicle speed sensor 34 is obtained, the rotational speed of the cooling fan 4 may be obtained by retrieving the rotational speed of the cooling fan 4 from the storage means. Alternatively, the rotational speed of the cooling fan 4 may be calculated by substituting the detected speed of the vehicle speed sensor 34 in a predetermined formula.

After the rotational speed of the cooling fan 4 is calculated, the control circuit 32 compares the calculated rotational speed of the cooling fan 4 and the rotational speed of the pump motor 6, and when the rotational speed of the cooling fan 4 is the rotational speed of the pump motor 6 obtained from the frequency generator 37 or lower, the control circuit 32 determines that the cooling fan 4 does not have the assist ability (“NO” in step a6: the determining means), and brings the electromagnetic clutch 21 into the disconnected state (step a7). When the rotational speed of the cooling fan 4 exceeds the rotational speed of the pump motor 6, the control circuit 32 determines that the cooling fan 4 has the assist ability (“YES” in step a6: the determining means) and brings the electromagnetic clutch 21 into the connected state (step a8).

Fourth Embodiment

FIGS. 9-11 show a fourth embodiment of the present invention. This embodiment differs from the above described first embodiment in the point that the cooling fan 4 is mounted on the rotor shaft 12 of the pump motor 6 via a one-way clutch 39 as shown in FIG. 9. As a one-way clutch 39, for example, a one-way ball clutch, a one-way roller clutch and the like are conceivable. In this embodiment, the electromagnetic clutch 21 is a main clutch, and the one-way clutch is an auxiliary clutch. As a control configuration, the vehicle speed sensor 34 is not provided as shown in FIG. 10.

In an electromagnetic clutch control routine shown in FIG. 11, the control circuit 32 conducts only the control of connecting and disconnecting the electromagnetic clutch 21 in accordance with the temperature of the liquid coolant in the outlet port 2 a of the jacket 2. Specifically, when the detected temperature of the liquid temperature sensor 33 is lower than the predetermined temperature T (“NO” in step B3) the control circuit 32 brings the electromagnetic clutch 21 in a disconnected state (step B4), and when the detected temperature of the liquid temperature sensor 33 is the predetermined temperature T or higher (“YES” in step B3) the control circuit 32 brings the electromagnetic clutch 21 into a connected state (step B4).

The operation of transmitting or not transmitting the rotation of the cooling fan 4 to the pump motor 6 in accordance with the presence or absence of the assist ability of the cooling fan 4 is automatically performed in accordance with the rotational speed of the cooling fan by the operation of the one-way clutch 39. The one-way clutch 39 has the function of transmitting only the rotation in one direction of the cooling fan 4 with respect to the rotor shaft 12 of the pump motor 6 to the rotor shaft 12. By this function, the one-way clutch 39 automatically transmits the rotation of the cooling fan 4 to the rotor shaft 12 to assist the pump motor 6, when the cooling fan 4 rotates in one direction relatively with respect to the rotor shaft 12 as a result of the rotational speed of the cooling fan 4 which rotates by receiving the driving wind pressure exceeding the rotational speed of the rotor shaft 12 of the pump motor 6 when the electromagnetic clutch 21 is in the disconnected state.

Fifth Embodiment

FIG. 12 shows a fifth embodiment of the present invention. This embodiment differs from the above described first embodiment in the point that transmission of rotation to the impeller 14 of the water pump 5 from the rotor shaft 12 of the pump motor 6 is performed by a magnetic coupling.

Specifically, as shown in FIG. 12, the rotor shaft 12 of the pump motor 6 is separated from the water pump 5 side. A cylindrical wall 17 a is formed in a center side of the partition plate 17 between the water pump 5 and the pump motor 6, and a boss portion 17 b is formed inside the cylindrical wall 17 a. A support shaft 40 is fitted in the boss portion 17 b of the partition plate 17, and the impeller 14 is rotatably supported by the support shaft 40 via a bearing 41.

A magnetic coupling 43 which transmits the rotation of the rotor shaft 12 to the impeller 14 is constituted of two large and small permanent magnet rings 44 and 45 differing in diameter. The permanent magnet rings 44 and 45 are made by being magnetized so that N-poles and S-poles are alternately arranged along the circumferential direction. The permanent magnet ring 44 on the large-diameter side is fitted to the inside of a cylindrical portion 46 provided at the rotor core 11 a of the rotor 11 of the pump motor 6, whereas the permanent magnet ring 45 on the small diameter side is fitted to the outside of a cylindrical portion 47 provided at the impeller 14. These permanent magnet rings 44 and 45 are opposed to each other via the cylindrical wall 17 a of the partition plate 17 to exert their magnetic forces onto each other. By the magnetic attraction forces of the permanent magnet rings 44 and 45, the rotation of the rotor 11 is transmitted to the impeller 14.

According to the embodiment in this configuration, a space between the water pump 5 and the pump motor 6 can be completely sealed by the partition plate 17 and the support shaft 40. Accordingly, leakage of the liquid coolant can be completely eliminated. As compared with the first embodiment which uses the mechanical seal 15 having the sliding portion, friction loss by the seal can be reduced.

Sixth Embodiment

FIG. 13 shows a sixth embodiment of the present invention. The sixth embodiment differs from the above described first embodiment in the point that an auxiliary cooling fan 48 is provided separately from the cooling fan 4 to cool the radiator 3. The auxiliary cooling fan 48 is also driven by a motor, and a motor generator 49 is used as a motor. The motor generator 49 is constituted of a permanent magnet type DC motor, and functions as both a motor and a generator.

The motor generator 49 is mounted on the radiator 3 via a support arm 50, and when the radiator 3 needs to be forcefully cooled, the motor generator 49 is switched on to function as a motor and rotationally drives the auxiliary cooling fan 48. When the auxiliary cooling fan 48 does not need to be driven, the motor is switched off and the auxiliary cooling fan 48 is rotationally driven by the driving wind, whereby the motor generator 49 functions as a generators The power generated by the motor generator 49 at this time is used to charge the battery 36. It is preferably determined in accordance with the vehicle speed whether the auxiliary cooling fan 48 has the assist ability or not, but the determination is not limited to this.

Other Embodiments

The present invention is not limited to the embodiments described above and shown in the drawings, but expansion or modification as follows is possible.

The rotational speed of the pump motor 6 may be changed in accordance with the detected temperature of the liquid temperature sensor 33. By doing so, the higher the temperature of the liquid coolant is, the more frequently the liquid coolant is circulated and the higher the rotation speed of the cooling fan 4 becomes, and therefore cooling of the liquid coolant is favorably performed.

The liquid temperature sensors which detect the temperature of the liquid coolant are provided at the outlet port 2 a and the inlet port 2 b of the jacket 2 of the engine 1, and the rotational speed of the pump motor 6 may be changed in accordance with the detected temperature difference of both the liquid temperature sensors. By doing so, the circulation amount of the liquid coolant can be changed in correspondence with the required cooling intensity, and the radiator 3 can be cooled with cooling air at a wind velocity corresponding to the required cooling intensity by rotating the cooling fan 4 at a speed corresponding to the cooling intensity.

The position in which the liquid temperature sensor 33 is provided is not limited to the outlet port 2 a or the inlet port 2 b of the jacket 2, but may be provided at the radiator 3, the thermo valve 27 and the like. The liquid temperature sensor 33 is provided so as to be in contact with the liquid coolant, and may directly detect the temperature of the liquid coolant or may detect it via a wall of a flow passage of the liquid coolant.

Actuation of the pump motor 6 may be delayed for a predetermined short time period from the point of time of start of the engine 1. By doing so, since tremendous power is required for actuation of the starter motor at the time of starting the engine 1, power at the time of actuating the pump motor 6 is not superimposed on this.

The pump motor 6 is not limited to an electric motor, but may be a motor with another mechanism such as a hydraulic motor.

In the sixth embodiment of FIG. 13, the auxiliary cooling fan 48 may cool a separate cooled body from the radiator 3, for example, a condenser of an air conditioner, for example. 

1. An engine cooling system for a vehicle, comprising: a water pump for circulating liquid coolant of an engine which is a propulsion source of the vehicle; a pump motor which drives the water pump; a temperature detecting means for detecting the temperature of the liquid coolant; a radiator which cools the liquid coolant circulated by the water pump; a cooling fan which cools the radiator; a clutch which connects and disconnects the cooling fan to and from the pump motor; an assist ability detecting means which detects whether or riot the cooling fan has assist ability of giving a rotational force to the pump motor when the cooling fan is rotated by receiving external wind dynamic pressure; and a control means which controls the clutch, wherein the control means causes the clutch to perform a connecting operation to connect the pump motor and the cooling fan when a detected temperature of the temperature detecting means is equal to or higher than a predetermined temperature, and when the detected temperature of the temperature detecting means is lower than the predetermined temperature and the assist ability detecting means detects presence of the assist ability, and the control means causes the clutch to perform a disconnecting operation to disconnect the pump motor from the cooling fan when the detected temperature of the temperature detecting means is lower than the predetermined temperature and the assist ability detecting means detects absence of the assist ability.
 2. The engine cooling system for a vehicle according to claim 1, wherein the assist ability detecting means comprises: a vehicle speed sensor which detects the speed of the vehicle; and a judging means which judges that the assist ability is present when a detected speed of the vehicle speed sensor is equal to or higher than a predetermined speed, and judges that the assist ability is absent when the detected speed of the vehicle speed sensor is lower than the predetermined speed.
 3. The engine cooling system for a vehicle according to claim 1, wherein the assist ability detecting means comprises: a motor rotational speed detecting means which detects the rotational speed of the pump motor; a vehicle speed sensor which detects the speed of the vehicle; and a judging means which calculates to convert a detected speed of the vehicle speed sensor into a rotational speed of the cooling fan, and judges that the assist ability is present when the calculated rotational speed is beyond the rotational speed of the pump motor detected by the motor rotational speed detecting means, and judges that the assist ability is absent when the rotational speed of the cooling fan is equal to or less than the rotational speed of the pump motor.
 4. The engine cooling system for a vehicle according to claim 1 wherein the assist ability detecting means comprises: a fan rotational speed detecting means which detects the rotational speed of the cooling fan; a motor rotational speed detecting means which detects the rotational speed of the pump motor; a vehicle speed sensor which detects the speed of the vehicle; and a judging means which judges that the assist ability is present when the rotational speed of the cooling fan detected by the fan rotational speed detecting means is beyond the rotational speed of the pump motor detected by the motor rotational speed detecting means, and judges that the assist ability is absent when the vehicle speed sensor detects a speed that is equal to or less than a predetermined speed.
 5. An engine cooling system for a vehicle, comprising: a water pump for circulating liquid coolant of an engine which is a propulsion source of the vehicle; a pump motor which drives the water pump; a temperature detecting means for detecting the temperature of the liquid coolant; a radiator which cools the liquid coolant; circulated by the water pump; a cooling fan which cools the radiator; a clutch which connects and disconnects the cooling fan to and from the pump motor; a control means which causes the clutch to perform a connecting operation to connect the pump motor and the cooling fan when a detected temperature of the temperature detecting means is equal to or higher than a predetermined temperatures and causes the clutch to perform a disconnecting operation to disconnect the pump motor from the cooling fan when the detected temperature of the temperature detecting means is lower than the predetermined temperature; and a one-way clutch which is provided between the pump motor and the cooling fan, connects the cooling fan to the pump motor when the cooling fan receives external wind dynamic pressure and tends to rotate faster than the pump motor, and cuts the connection of the cooling fan and a rotor shaft of the pump motor when a rotational speed of the cooling fan which rotates by receiving the external air pressure is lower than the rotational speed of the pump motor.
 6. The engine cooling system for a vehicle according to claim 1, wherein the rotational speed of the pump motor is controlled to be changed in accordance with the detected temperature of the temperature detecting means.
 7. The engine cooling system for a vehicle according to claim 5, wherein the rotational speed of the pump motor is controlled to be changed in accordance with the detected temperature of the temperature detecting means.
 8. The engine cooling system for a vehicle according to claim 1, wherein the rotational speed of the pump motor is controlled to be changed in accordance with the difference in temperature of the liquid coolant on an inlet port side and an outlet port side of the engine.
 9. The engine cooling system for a vehicle according to claim 5, wherein the rotational speed of the pump motor is controlled to be changed in accordance with the difference in temperature of the liquid coolant on an inlet port side and an outlet port side of the engine.
 10. The engine cooling system for a vehicle according to claim 1, wherein transmission of rotation from the pump motor to the water pump is performed by a magnetic coupling.
 11. The engine cooling system for a vehicle according to claim 5, wherein transmission of rotation from the pump motor to the water pump is performed by a magnetic coupling.
 12. The engine cooling system for a vehicle according to claim 1, wherein the pump motor is configured to be actuated behind a starting Lime of the engine.
 13. The engine cooling system for a vehicle according to claim 5, wherein the pump motor is configured to be actuated behind a starting time of the engine.
 14. The engine cooling system for a vehicle according to claim 1, wherein a further cooling fan for cooling the radiator or a body to be cooled other than the radiator is provided separately from the cooling fan, and a further motor which drives the further cooling fan is constituted of a motor generator which functions as a generator when receiving a rotational force from the further fan and the further cooling fan does not need to be driven.
 15. The engine cooling system for a vehicle according to claim 5, wherein a further cooling fan for cooling the radiator or a body to be cooled other than the radiator is provided separately from the cooling fan, and a further motor which drives the further cooling fan is constituted of a motor generator which functions as a generator when receiving a rotational force from the further fan and the further cooling fan does not need to be driven. 